A zinc oxide surge arrester is an overvoltage protection apparatus. The properties of a zinc oxide surge arrester valve block, as a core component of the zinc oxide surge arrester, have a direct influence on the use of the surge arrester, and the effectiveness of a side insulating coating directly determines the capability of the surge arrester to withstand a large current surge. At present, side coating materials for the valve blocks of zinc oxide surge arresters include lead-containing side glazes, organic coatings represented chiefly by epoxy coatings and organosilicon coatings, and conventional inorganic coatings.
Since the main component of lead-containing side glaze is PbO, and PbO is a toxic substance which readily volatilizes when a green body is processed or sintered at high temperature, such a glaze will cause long-term irreversible harm to human society and the natural world, and is not in conformity with the environmentally friendly development trend of today's world.
With regard to organic coatings, since they do not bind well to resistor element green bodies, surfaces readily adsorb water or bubbles form thereon, with the result that such coatings have poor ability to withstand overvoltage. In addition, there is a large difference between the thermal expansion coefficient of an epoxy coating and that of a resistor element green body; when subjected to an impulse; epoxy resin might crack, resulting in arc-over of the side insulating coating. The temperature of use of organic coatings is not high, and this has limited the range of uses of this type of zinc oxide resistor element to a certain extent.
A conventional inorganic coating can only be applied once the resistor element green body has been pre-baked. This brings about the problem of secondary sintering; compared with other processes, there is an additional process step, and the result is that the process is complicated, the number of sintering operations is increased, and the sintering time is extended. There is impaired control over the stability of the various electrical properties of the resistor element, and a huge amount of electrical energy is wasted, which is not good for environmental protection, and also not good for the energy-saving and emission-reduction requirements of industrial production.